Motor armature having distributed windings for reducing arcing

ABSTRACT

An armature for a brush commutated electric motor having a distributed coil winding arrangement for reducing brush arcing and electromagnetic interference (EMI). The winding pattern involves segmenting each coil into first and second subcoil portions with differing pluralities of turns. Each subcoil portion is wound around separate pairs of spaced apart slots of a lamination stack. Adjacent coils are wound such that one subcoil portion of each is wound in a common slot to therefore form an overlapping arrangement of each pair of adjacently coils. The winding pattern serves to “shift” the resultant magnetic axes of each coil in such a manner so as to significantly reduce brush arcing and the EMI resulting therefrom. The reduction in EMI is sufficient to eliminate the need for EMI reducing components, such as chokes, which have typically been required to maintain EMI to acceptably low levels. Commutation efficiency is also improved by the distributed winding pattern described above because of the reduction in the unevenness of the magnetic coupling between adjacent coils.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 10/404,857, filed onApr. 1, 2003 and presently, which is a divisional of U.S. Ser. No.09/594,357, filed Jun. 14, 2000, which issued as U.S. Pat. No. 6,566,782on May 20, 2003.

TECHNICAL FIELD

This invention relates to electric motors, and more particularly to awinding pattern for winding the coils on an armature in a manner toreduce electromagnetic interference and arcing at the brushes in contactwith the commutator of the armature.

BACKGROUND OF THE INVENTION

Present day brush commutated electric motors include an armature havinga plurality of coils wound in slots formed in the lamination stack ofthe armature. With traditional motor designs, the lamination stack ofthe armature forms a plurality of circumferentially arranged slotsextending between adjacent pairs of lamination posts. Typically, twocoils per slot are used when winding the armature coils on thelamination stack. Among the two coils of the same slot, the one whichcommutates first is referred to as the first coil and the one whichcommutates second as the second coil. The second coil has inherentlypoorer magnetic commutation than the first coil because the second coilpasses beyond the magnetic neutral zone within the stator before itfinishes commutation. This is illustrated in simplified fashion in FIG.1, wherein the commutation region of the first coil is designated by Z₁and the commutation region of the second coil is designated by Z₂. Arotor “R” is shown positioned within a stator “S” having field coils“F”. This is further illustrated in FIGS. 1 a-1 f. FIGS. 1 a and 1 billustrate the position of the magnetic axis of the first and secondcoils, respectively, relative to the commutation regions Z₁ and Z₂ ofeach coil. FIGS. 1 c and 1 d illustrate the position of the magneticaxis of each of the first and second coils, relative to the field poleand brush, at the start of commutation of each coil. The magnetic axisof the first coil, in this example, is retarded about 22.5 degrees fromthe axis of the field pole and the brush (FIG. 1 c), while for thesecond coil, its magnetic axis is only retarded about 7.5 degreesrelative to the field pole and brush (FIG. 1 d). FIG. 1 e shows theangular position of the magnetic axis of the first coil, relative to thefield pole, when the first coil ends commutation. FIG. 1 f shows theangular position of the magnetic axis of the second coil, relative tothe field pole and brush, when the second coil ends commutation. Theangular position of the second coil, when it ends commutation, isclearly past the angular position, relative to the field pole, at whichthe first coil ends its commutation. The two regions Z₁ and Z₂ are notcommonly angularly aligned (i.e., coincident) relative to the field poleand brush. As a result, the second coil commutation can generatesignificant brush arcing, and becomes the dominant source of the totalbrush arcing of the motor. This can also cause electro-magneticinterference (EMI) to be generated which exceeds acceptable levels setby various government regulatory agencies. This brush arcing can alsolead to accelerated brush wear.

Accordingly, it is a principal object of the present invention toprovide an armature for a brush commutated electric motor having aplurality of coils wound thereon in a unique sequence which serves tosignificantly reduce brush arcing and improve the commutation efficiencyof the motor.

It is a further object of the present invention to provide an armaturefor a brush commutated electric motor which incorporates a uniquewinding pattern for the coils wound on the armature in a manner whichdoes not otherwise require modification of any component of the armatureor the need for additional components.

It is still a further object of the present invention to provide awinding pattern for the armature coils of an armature which allows EMIcomponents usually required to sufficiently attenuate the EMI generatedby brush arcing to be eliminated, thus allowing the motor to beconstructed less expensively and with fewer components.

SUMMARY OF THE INVENTION

The above and other objects are provided by an armature for a brushcommutated electric motor incorporating a unique, distributed windingpattern for the coils thereof, in accordance with a preferred embodimentof the present invention. The winding pattern involves segmenting eachcoil into first and second subcoil portions. With a first coil, thefirst subcoil portion is wound around two spaced apart slots for a firstplurality of turns and the second subcoil portion is wound around asecond pair of spaced apart slots which are shifted circumferentiallyfrom the first pair of slots. The second subcoil portion is also formedby a different plurality of winding turns than the first subcoilportion. The two subcoil portions are wound in series with one endcoupled to a first commutator segment of the armature and the other endcoupled to a second commutator segment.

A second coil is also divided into first and second subcoil portions,with the first subcoil portion being wound with the same number of turnsas the second subcoil portion of the first coil, and in the second pairof spaced apart slots. The second subcoil portion of the second coil,however, is laterally shifted such that it is wound in a third pair ofspaced apart slots shifted laterally by one slot from the second pair ofslots. The second subcoil portion of the second coil is also wound aplurality of turns in accordance with that of the first portion of thefirst coil. One end of the first subcoil portion of the second coil iscoupled to commutator segment number two while the end of subcoilportion two of coil two is coupled to commutator segment number three.

Coil number three is segmented into first and second subcoil portionswith the first subcoil portion being wound a number of turns inaccordance with the second subcoil portion of the second coil, and woundaround the second pair of spaced apart slots. The second subcoil portionof the third coil is wound around the third pair of spaced apart slotsbut with a number of turns in accordance with the first subcoil portionof the second coil. The end of the first subcoil portion of the thirdcoil is coupled to commutator segment number three while the end of thesecond subcoil portion of coil three is coupled to commutator segmentnumber four.

The above winding pattern continues in alternating fashion such that anoverlapping of the coils occurs around the lamination stack. In effect,all of the first subcoil portions shift their magnetic axes forward withrespect to rotation of the armature, and all of the second coil portionsshift their magnetic axes backward relative to the direction of armaturerotation. With a desired turns ratio between the two subcoil portions ofeach coil, which ratio may vary considerably but is preferably about3:1, the above described winding pattern smoothes out the “unevenness”in the magnetic coupling between adjacent armature coils, thus improvingcommutation efficiency. This also improves the commutation efficiencyfor the second subcoil portion of each coil, thus reducing brush arcing.This in turn serves to significantly reduce EMI. The reduction of EMIeliminates the need for expensive EMI suppression components that havepreviously been required for use with the motor brushes to ensure thatEMI levels remain below regulated limits.

BRIEF DESCRIPTION OF THE DRAWINGS

The various advantages of the present invention will become apparent toone skilled in the art by reading the following specification andsubjoined claims and by referencing the following drawings in which:

FIG. 1 is a simplified diagrammatic end view of an armature having atraditional coil winding pattern employed, and illustrating how thecommutation zone of the second coil of a two-coil-per-slot windingarrangement causes the commutation zone of the second coil to lag behindthe commutation zone of the first coil, thus leading to brush arcing;

FIGS. 1 a-1 f illustrate a prior art winding pattern showing how twocoils of a coil pair produce non-coincident commutation regions;

FIG. 2 is a side elevational view of an exemplary armature constructedin accordance with the teachings of the present invention;

FIG. 3 is a simplified cross sectional end view of the armature of FIG.2 illustrating a lamination stack for an armature having a plurality oftwelve slots around which the coils of the armature are to be wound;

FIG. 4 illustrates in simplified fashion a coil winding pattern inaccordance with the present invention; and

FIG. 5 is a simplified end view of the armature illustrating how thewinding pattern produces commutation zones for the first and second coilwith subcoil portions which are radially aligned with one another toimprove commutation efficiency and reduce brush arcing.

FIGS. 5 a-5 c and 6 a-6 c illustrate the angular positioning of theresultant magnetic axis of each coil of a given coil pair, relative tothe position of the commutator bars to which the coils are attached, atthe start of commutation, at the end of commutation, and at anintermediate point during commutation;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 2, there is shown an armature 10 for a brushcommutated electric motor 11 having a plurality of coils wound inaccordance with the teachings of the present invention. The armature 10includes a commutator 12 which, merely by way of example, includes 24independent commutator segments 12 ₁-12 ₂₄. A lamination stack 14 isused to support a plurality of 24 coils 25 ₁-25 ₂₄ wound thereon. Anarmature shaft 22 extends through the lamination stack 14 and is fixedlycoupled to a gear reduction assembly 20 and also to a fan 18. It will beappreciated, though, that the fan 18 and the gear reduction assembly 20are optional and not essential to the armature 10 of the presentinvention, and shown merely because they are components that are oftenused in connection with an armature for an electric motor.

Referring to FIG. 3, the lamination stack 14 is illustrated without anycoils wound thereon. The lamination stack 14 includes a plurality ofradially projecting lamination posts or “teeth” 24. Twelve slots S₁-S₁₂are formed between the posts 24. It will be appreciated immediately,however, that while twelve such slots are illustrated, that a greater orlesser plurality could be employed. The overall number of slots dependson the number of commutator segments and will always be one-half thenumber of commutator segments used.

Referring now to FIG. 4, the winding pattern of the present inventionwill be described. Coil number 1 (25 ₁) has a first subcoil portion 1Aand a second subcoil portion 1B formed in series with subcoil portion1A. Subcoil portion 1A has one end thereof coupled to commutator segmentnumber 12 ₁ and the end of second subcoil portion 1B is coupled tocommutator segment number 12 ₂. Subcoil portion 1A of coil 25 ₁ includesa first plurality of turns, for example seven turns, which are woundaround slots S₁₂ and S₅ of the lamination stack 14. Subcoil portion 1Bof coil 25 ₁ is then wound for a larger plurality of turns, in thisexample 17 turns, in slots S₁ and S₆ of the lamination stack 14. It willbe appreciated that the precise number of windings of each subcoilportion can vary considerably, but in the preferred embodiment thenumber of turns between the subcoil portion 1B and portion 1A of coil 25₁ is such that one has preferably about three times as many windingturns as the other. The number of turns also alternates between thesubcoils, as will be described further, such that adjacent coils willalways have the two first subcoil portions with differing numbers ofwinding turns, and the two second subcoil portions with differingnumbers of winding turns.

Coil number 2 (25 ₂) also has a first subcoil portion 2A and a secondsubcoil 2B in series with one another. Subcoil portion 2A is wound inslots S₁ and S₆ with seventeen turns. Subcoil portion 2B is wound inseries with portion 2A but around slots S₅ and S₇ of the laminationstack 14, and with seven winding turns. The end of subcoil portion 2A iscoupled to commutator segment 12 ₂ while the end of subcoil portion 2Bis coupled to commutator segment 12 ₃. The first subcoil portion 2A ofcoil 25 ₂ overlaps the second subcoil portion 1B of coil 25 ₁.

Coil number 3 (25 ₃) includes a first subcoil portion 3A and a secondsubcoil portion in series with one another 3B. Subcoil portion 3A isattached to commutator segment number 12 ₃ and includes seven windingturns wound around slots S₁ and S₆. Subcoil portion 3B is formed inseries with subcoil portion 3A and includes seventeen turns wound inslots S₂ and S₇, with the end thereof being coupled to commutatorsegment 12 ₄.

Coil 4 (25 ₄) also includes a first subcoil portion 4A and a secondsubcoil portion 4B in series with subcoil portion 4A. Subcoil portion 4Ahas its end coupled to commutator segment 12 ₄ and includes seventeenturns wound around slots S₂ and S₇. Subcoil portion 4B includes seventurns wound around slots S₃ and S₈, with the end thereof being coupledto commutator segment 12 ₅. It will be noted that coil 25 ₄ partiallyoverlaps coil 25 ₃. In effect, one of the subcoil portions of eachadjacent pair of coils 25 overlap with each other.

The above-described pattern for coils 25 ₁-25 ₄ is repeated until all ofthe coils (in this example 24 coils) are wound onto the lamination stack14. Each of the ends of the coils 25 ₁-25 ₂₄ are further secured toimmediately adjacent pairs of commutator segments 12 ₁-12 ₂₄. Forexample, coil 25 ₅ has its ends secured to commutator segments 12 ₅ and12 ₆, coil 25 ₆ to segments 12 ₆ and 12 ₇, and so forth.

The above-described winding pattern significantly improves thecommutation performance of all of the second coil portions of the coils25. Splitting each coil 25 into first and second subcoil portions allowseach first subcoil portion to shift its magnetic axis away (i.e.,laterally), from the position it would have otherwise had in atraditional two-coil-per-slot. This is illustrated in FIGS. 5 a-5 c andFIGS. 6 a-6 c. These figures each show a coil consisting of two seriesconnected subcoils of unequal turns as disclosed previously. Eachsubcoil has a magnetic axis as shown. The resultant magnetic axis of thecomplete coil resides between the magnetic axes of the subcoils, but itis closer to the larger of the two. In FIGS. 5 a and 6 a, theorientation of the resultant magnetic axis of each of coils 1 and 2 (25₁ and 25 ₂) can be seen to fully overlap, as evidenced by the alignmentof commutation regions 30 and 32 for each of the two coils 1 and 2.

In FIGS. 5 b and 6 b, each of coils 1 and 2 are shown at the beginningof commutation. In FIG. 5 b, the resultant magnetic axis of coil 1 isshifted laterally to the right in the drawing figure due to theweighting of the turns of the two subcoil portions of coil 1. Itsresultant magnetic axis aligns with the beginning of commutation region30 of coil 1 as indicated by the vertical line 36. In this example, theresultant magnetic axis of coil 1 is advanced 15 degrees, or one-halfthe width of the commutation region 30. The axis of the field pole canbe seen to fall at the center of brush 40. In FIG. 6 b, the resultantmagnetic axis of coil 2 is shifted laterally to the left due to theweighting of the two subcoil portions of coil 2. The resultant magneticaxis of coil 2 thus also aligns with vertical line 36 at the beginningof commutation of coil 2. As such, both of coils 1 and 2 begincommutation at the same angular point (i.e. represented by line 36)relative to the axis of the field pole and the brush 40.

In FIGS. 5 c and 6 c, each of coils 1 and 2 are shown at the end oftheir respective commutation regions 30 and 32. In FIG. 5 c, theresultant magnetic axis of coil 1 is indicated by the vertical line 38.In FIG. 6 c, the resultant magnetic axis of coil 2 falls at the sameangular position as coil 1, as also indicated by vertical line 38.Commutation regions 30 and 32 fully overlap one another, as evidenced inFIGS. 5 b, 6 b and 5 c, 6 c, and are in a common overlapping region withrespect to the field coil 34 shown in FIG. 5.

Further, it can be seen by examining FIGS. 5, 5 a-5 c and 6 a-6 c thatthe commutation regions 30 and 32 are also in a common angular positionwith respect to the commutator bars 12 to which the coils are connected.With a turns ratio between the two subcoils of about 3:1, this windingpattern smoothes out the magnetic “unevenness” between adjacent coils,which is a drawback with traditional two-coil-per-slot winding patterns.This, in connection with the shifting of the resultant magnetic axes ofeach coil, serves to significantly improve the commutation efficiency ofthe motor and to reduce the overall brush arcing.

The winding pattern employed on the armature 10 of the present inventionalso serves to significantly reduce the cost of constructing thearmature by eliminating components that would otherwise be needed tosufficiently attenuate the EMI that results from traditionaltwo-coil-per-slot winding patterns. Typically, inductive components arerequired to form a choke circuit associated with each armature brush.These additional components increase the overall cost of manufacturing amotor, as well as increase the complexity of the task of replacing thebrushes during repair procedures.

The apparatus and method of the present invention thus allows anarmature to be formed which significantly reduces brush arcing, andtherefore the EMI that is present with traditional two-coil-per-slotarmature constructions for all brush commutated electric motors. Theapparatus and method of the present invention further does not increasethe complexity of the manufacturing process or require additionalcomponent parts that would otherwise increase the overall cost ofconstruction of an armature.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the present invention can beimplemented in a variety of forms. Therefore, while this invention hasbeen described in connection with particular examples thereof, the truescope of the invention should not be so limited since othermodifications will become apparent to the skilled practitioner upon astudy of the drawings, specification and following claims.

1. An electric motor comprising: an armature having a plurality ofspaced-apart posts defining a plurality of winding slots therebetween; acommutator having a plurality of commutator bars that number twice thatof said winding slots; at least one brush disposed adjacent saidcommutator; a stator disposed coaxially with the armature, said statorhaving a plurality of spaced apart field coils; said armature including:a first coil having a first subcoil portion and a second subcoil portionhaving differing numbers of turns; said first subcoil portion beingwound in a first pair of spaced apart ones of said slots; said secondsubcoil portion being wound in a second pair of spaced apart ones ofsaid slots that are offset from said first pair of spaced apart slots; asecond coil having a first subcoil portion and a second subcoil portionhaving differing numbers of turns; said first subcoil portion of saidsecond coil being wound in said second pair of spaced apart slots so asto overlap said second subcoil portion of said first coil; said secondsubcoil portion of said second coil being wound in a third pair ofspaced apart ones of said slots offset from said second pair of spacedapart slots; wherein both of said coils begin commutation at the sameangular position relative to said brush; and wherein both of said coilsend commutation at the same angular position relative to said brush. 2.The electric motor of claim 1, wherein one of said first and secondsubcoil portions of said first coil has approximately three times anumber of winding turns as the other.
 3. The electric motor of claim 1,further comprising a third coil having first and second subcoil portionsthat are wound in the same said slots as said subcoil portions of saidsecond coil.
 4. An electric motor having an armature, the electric motorcomprising: a lamination stack having a plurality of radially extendingposts, said posts forming a plurality of slots therebetween, said slotsbeing arranged in a circumferential pattern; a plurality of coils woundaround said slots, said coils being arranged in pairs about saidlamination stack; each said coil being divided into first and secondsubcoil portions, with said first subcoil portion having a firstplurality of winding turns and said second subcoil portion having asecond plurality of winding turns, and wherein said first and secondsubcoil portions are wound in different, circumferentially offset pairsof said slots and coupled to designated pairs of commutator segments ofa commutator; wherein a first pair of said coils are wound in anoverlapping fashion such that the first subcoil portion of a second oneof said first pair of coils is wound in the same slots as said secondsubcoil portion of a first one of said first pair of coils, and saidsecond subsoil portion of said second one of said first pair of coils iswound in a pair of slots offset by one slot position from said slotsthat said second subcoil portion of said first one of said first pair ofcoils is wound in; and wherein a second pair of coils circumferentiallyoffset from said first pair of coils is further wound such that a firstsubsoil portion of a first one of said second pair of coils is wound inthe same slots as said first subcoil portion of said second coil of saidfirst pair of coils, and said second subcoil portion of said first oneof said second one of second pair of coils is wound in the same slots assaid second subsoil portion of said second coil of said first pair ofcoils; and wherein a resultant magnetic axis of each said coil is at thesame angular position relative to the pair of commutator segments towhich each said coil is secured; and wherein said same angular positionenables coincident commutation zones to be formed for each of saidcoils.
 5. The electric motor of claim 4, wherein one of said first andsecond subcoil portions of each said coil has a greater number ofwinding turns that the other of said subcoil portions.
 6. The electricmotor of claim 4, wherein one of said first and second subcoil portionsof each said coil has approximately three times the number of windingturns as the other of said subcoil portions.
 7. An electric, rotatingmachine comprising: a stator having a plurality of field coils, whereinsaid field coils are spaced apart to form gaps therebetween; an armaturehaving a plurality of coils wound thereon such that a magnetic axis of afirst one of said coils is advanced, relative to a given pair of saidfield coils when said first coil is excited, and a magnetic axis of asecond one of said coils is retarded, relative to said given pair offield coils when said second coil is excited; and wherein said first andsecond coils complete commutation while passing through coincidentangular regions relative to said brush.
 8. The machine of claim 7,wherein each of said first and second coils is segmented into twosubcoil portions coupled in series.
 9. The machine of claim 8, whereinsaid subcoil portions of said first and second coils are wound such thatat least one of said subcoil portions of each are wound in a common pairof slots of said armature.
 10. An electric motor comprising: an armaturehaving a plurality of spaced apart posts defining a plurality of spacedapart winding slots; a stator disposed coaxially with the armature, saidstator having a plurality of spaced apart field coils defining anangular region between each adjacent pair of said field coils; saidarmature including: a first coil having a first subcoil portion and asecond subcoil portion; said first subcoil portion having a firstplurality of winding turns and being wound in a first pair of spacedapart ones of said slots; said second subcoil portion having a secondplurality of winding turns and being wound in a second pair of spacedapart ones of said slots that are offset from said first pair of spacedapart slots; a second coil having first and second subcoil portionswound in third and fourth pairs, respectively, of spaced apart ones ofsaid slots; wherein said subcoils of said first coil are wound withdifferent numbers of winding turns to shift a resultant magnetic axis ofsaid first coil so that said resultant magnetic axis lies at a firstpredetermined angular position relative to a first pair of commutatorbar to which said first coil is secured; wherein said subcoils of saidsecond coil are wound with differing numbers of turns to align aresultant magnetic axis of said second coil at a second predeterminedangular position to a second pair of commutator bars to which saidsecond coil is secured; and wherein said first and second predeterminedangular positions define the same angular position, and wherein saidcoils have coincident commutation regions.
 11. An electric motor ofclaim 10, wherein said subcoil portions of each said coil have differingnumbers of winding turns.
 12. An electric motor comprising: an armaturehaving a plurality of spaced apart posts defining a plurality of spacedapart winding slots; a stator disposed coaxially with the armature, saidstator having a plurality of spaced apart field coils defining anangular region between each adjacent pair of said field coils; saidarmature including: a first coil having a first subcoil portion and asecond subcoil portion; said first subcoil portion having a firstplurality of winding turns and being wound in a first pair of spacedapart ones of said slots; said second subcoil portion having a secondplurality of winding turns and being wound in a second pair of spacedapart ones of said slots that are offset from said first pair of spacedapart slots; a second coil having first and second subcoil portionswound in third and fourth pairs, respectively, of spaced apart ones ofsaid slots; wherein a resultant magnetic axis of said first coil ispositioned at a first angular point relative to a pair of commutatorbars to which said first coil is coupled; wherein a resultant magneticaxis of said second coil is positioned at a second angular pointrelative to a pair of commutator bars to which said second coil iscoupled, said first and second angular points defining the same angularpoint; and wherein both of said coils begin and complete commutationwithin a predetermined, coincident angular commutation region relativeto said given pair of field coils.
 13. The electric motor of claim 12,wherein said first and second subcoil portions of each of said first andsecond coils are wound with differing numbers of winding turns.